This invention relates to a method and to an apparatus for monitoring if wheels of a railway vehicle are round.
As manufactured, a wheel of a railway vehicle can be expected to be accurately round, but through use the wheel tread may develop uneven radial deformations so it is out of round. This may arise if a part of the tread wears more rapidly than other parts of the tread as a result of defects or non-uniform materials, or it may arise as the result of skidding on the rails, causing a flat, or due to defects in the suspension. In any event such out of round wheels are responsible for increased forces on both the vehicle suspension and on the railway track, which may lead to damage to the suspension components, and to degradation of the track. They cannot easily be detected without removing each wheel from the track (for example during maintenance). A way of monitoring if wheels are round without taking vehicles out of service would therefore be useful, particularly in planning maintenance.
According to the present invention there is provided a method of monitoring the shape of a wheel of a railway vehicle, while the wheel is rolling along a rail of a railway track, by measuring how far the flange of the wheel projects below the upper surface of the rail.
It has been found that the perimeter of railway wheel flanges are accurately round, and that the shape of the flange is very rarely affected by those problems which cause the wheel tread to become out of round. Hence the flange can be used as a measurement datum.
In a second aspect, the present invention also provides apparatus for monitoring the shape of a wheel of a railway vehicle, while the wheel is rolling along a rail of a railway track, the apparatus comprising means for measuring how far the flange of the wheel projects below the upper surface of the rail.
Preferably the apparatus comprises a rigid bar, and means to support the bar alongside the rail, the bar being supported resiliently so as to be depressed by a flange of a wheel, the support means being clamped to the rail, and the apparatus also comprises means to measure the vertical displacement of the bar. This ensures that any movement of the track bed does not affect the measurement.
In a preferred embodiment the support means is arranged so that all parts of the bar are at the same height above the underside of the rail. The support means may comprise a plurality of flat leaf springs connected to the bar, the springs being parallel to each other and inclined to the horizontal at an angle preferably between about 25xc2x0 and 40xc2x0, for example 30xc2x0. This ensures that the bar remains substantially parallel to its original position (and so to the top surface of the rail) when depressed, irrespective of the position along the bar at which the flange is in contact.
As the circumference of a wheel is typically greater than the wheelbase between successive wheels on a bogie of a vehicle it is desirable to provide a plurality of such bars alongside the rail. For example each bar might be of length about 0.7 m, the apparatus including for example five such bars.